1. Technical Field
The present invention relates to mobile communication systems and ranging methods thereof.
2. Discussion of the Related Art
Mobile communication devices, such as cell phones or personal digital assistants, enable users or subscribers to wirelessly connect with a communications network. In addition to voice or data communication capabilities, mobile communication devices may come equipped with supplemental functions such as reception for digital multimedia broadcasting (DMB), positioning, and so forth. Positioning (i.e., determining where a mobile communication device is located) can be used in a variety of applications. For example, positioning may be utilized in cases where people (including criminals) are missing.
For accurate positioning, distances are ranged in high fidelity. There are several known ranging techniques, some of which employ, e.g., Received-Signal Strength (RSS) and Time-Of-Arrival (TOA) modes. In the RSS mode, a distance is found from the strength (or energy level) of a received signal that is reflected off an object. For example, if the strength of the received signal is strong, the object is detected as being near the reception site, and if the received signal is weak, the object is detected as being apart therefrom.
In the TOA mode, a distance is obtained from an arrival time of a received signal that is reflected off an object. For example, a shorter arrival time indicates the object is near the reception site, while a longer arrival time indicates the object is far therefrom. Generally, the TOA mode provides higher accuracy for positioning or ranging than the RSS mode.
General standards for local wireless networks include wireless local area network (WLAN), Bluetooth, and ZigBee, for example. These wireless communication standards are generally not suited for the TOA mode because they have a weak resolution rate in the time domain. Time resolution means the minimum size of a signal distinguishable in the time domain. For this reason, most standards for wireless communication are adapting the RSS mode. However, as aforementioned, the RSS mode is inferior to the TOA mode in accuracy. Further, in general, the wireless communication standards are not adjusted to accommodate ranging a communication distance with high accuracy or resolvability. Therefore, a need exists for a technique capable of providing a highly accurate ranging.